The present invention relates generally to wireless communications, and more particularly to multiplexed coding design for cooperative communications.
In wireless communications, a transmitter typically transmits information to a receiver over a communication channel. Statistically, a communication channel can be defined as a triple consisting of an input alphabet, an output alphabet, and for each pair (i,o) of input and output elements of each alphabet, a transition probability p(i,o). The transition probability is the probability that the receiver receives the symbol o given that the transmitter transmitted symbol i over the channel.
Given a communication channel, there exists a number, called the capacity of the channel, such that reliable transmission is possible for rates arbitrarily close to the capacity, and reliable transmission is not possible for rates above the capacity
In some circumstances, the distance separating the transmitter (i.e., source) and the receiver (i.e., destination) is large. Alternatively or additionally, the communication channel over which the source and destination communicate may be of poor quality. As a result, interference may be introduced in the communications between the source and the destination, which can result in distortion of the message. To reduce the effect of interference, the transmitter and receiver often transmit information over a communication channel using a coding scheme. The coding scheme provides redundancy so that the message can be detected (and decoded) by the receiver in the presence of interference.
The coding scheme uses codes, which are an ensemble (i.e., group) of vectors that are to be transmitted by the transmitter. The length of the vectors are assumed to be the same and is referred to as the block length of the code. If the number of vectors is K=2k, then every vector can be described with k bits.
Employing multiple antennas in a mobile terminal to achieve transmit diversity or special diversity, known as multiple-input and multiple-output (MIMO), has become a promising solution to combat fading channels and potentially provide very high data rates. Recently, cooperative communication has drawn increasing interest in the wireless communication area due to user cooperation diversity or cooperative diversity gain, which is another form of spatial diversity created by using a collection of distributed antennas from multiple terminals in a network. User cooperation is a framework where two users can jointly transmit their signals, in coded cooperation, using both of their antennas. As shown in FIG. 1, with user cooperation, each user's transmission is receivable, to different degrees, by the other user as well as the receiver 106. Therefore, a user receives and re-transmits the data of another user to the receiver 106, thus providing assistance to the other user. Because the two messages are received via independent paths 108 and 110, the spatial diversity will provide an improvement in overall reception. As shown in FIG. 1, with user cooperation, a first user 102 and a second user 104 share their antennas to form a virtual antenna array providing the potential of realizing spatial diversity through distributed transmission and signal processing.
Two coding design methods, multiplexed coding and superposition coding, theoretically perform very well. However, practically, it is difficult to build or decode as well as theoretically described when implementing these coding schemes. These two schemes are very difficult to implement with practical codes.
Therefore, there remains a need to design a coding method which is easier to implement, but approaches the accuracy and rate of multiplexed coding.